The present invention relates to the field of drivetrains of vehicles, and more particularly, to a method for controlling and improving a launch of a vehicle, especially a utility vehicle provided with an exhaust gas recirculation (EGR).
In vehicles provided with an EGR today, a lower launching gear is selected when the EGR is activated, in comparison when the EGR is not activated. The lower launching gear is selected because of the power loss caused by the EGR. Thereby is an extra gear change necessary to launch the vehicle and reach a travelling speed. The extra gear change reduces the comfort and increases the stress and wear on the parts in the drivetrain, and is also not wanted in an environmental perspective.
Further, the power loss caused by the EGR has shown to be individual for each EGR, wherein a lower starting gear is chosen in cases in which it standard launching gear would have been possible.
There is, thus, a need for improvement, to keep the environmental benefits of the EGR without having the disadvantages of the lower launching gear.
It is desirable to provide an inventive method for launch of a vehicle with an exhaust gas recirculation (EGR) where the previously mentioned problems are partly avoided.
The method is applicable on a vehicle with a driveline, which at least comprises an engine, an automatic transmission and a system for exhaust gas recirculation (EGR). The driveline is controlled by a driveline management system (MS). The MS can comprise several different management systems, such as an engine management system and a transmission management system. The main functions of the vehicle are controlled by the MS, wherein for the present application, the MS has access to or is able to determine the mass of the vehicle. The MS uses the information about the mass of the vehicle to calculate a launching gear of the transmission. Systems for determining the mass of a vehicle is well know, such systems could be determining the mass of the vehicle during launch of the vehicle, or be mass sensor based systems or be any other system for determining the mass of the vehicle and from that information calculate a launching gear at least dependent of said determined mass.
The inventive method is characterised in, that a launching gear is chosen dependent of the power loss caused by the EGR. This is done, in that                the power loss caused by the EGR is determined,        the available power to launch the vehicle is determined, and        the launching gear is recalculated dependent of said available power, and        selecting said recalculated launching gear before launch of the vehicle.        launch the vehicle with said recalculated launching gear engaged.        
The system for EGR sends a signal comprising information of how much power that is lost when EGR is enabled during launch of the vehicle. The power loss is however dependent of the launching gear used during the launch, i.e. the speed of the engine, and the engine power, whereby the MS first determines the available power from the engine, for each possible launching gear. The MS then performs the same calculation operations for the available power when the EGR power loss for the individual gears is subtracted, wherein the highest gear possible with the FOR power loss subtracted is chosen. Whereby said recalculated launching gear is selected and engaged and the vehicle can be launched therewith.
Due to the inventive method the correct launching gear can be selected already before the first launch. Further, instead of consequently selecting a lower gear than calculated, the correct gear can always be chosen. Due to the presented inventive method, the driving comfort is increased and the vehicle is driven in a more environmental friendly manner, because less gear changes have to be made to reach the desired travel speed. A further advantage with a high launching gear is that the wear on the drivetrain will be reduced, since the vehicle can reach its travelling speed with less gear changes. The method further have the advantage, that the vehicle will be able to be launched during conditions, at which the available power to launch the vehicle normally would not be sufficient, such as during fully loaded vehicle launches in uphill slopes.
Further advantages are achieved by implementing one or several of the features of the dependent claims. In a first advantageous embodiment of the inventive method, an engagement of a starting clutch is controlled dependent of the power loss, which is caused by the EGR and said selected launching gear. By having a longer engagement time of the clutch, a higher gear than otherwise can be selected as launching gear for the vehicle.
In another advantageous embodiment of the invention the method further comprises: reducing the EGR during a slippage of said starting clutch, wherein the recirculation is not reduced more than to just allow launching the vehicle from a higher starting gear than otherwise. This measure is meant to be a complement, if the calculated available power is just below the limit for using a specific starting gear, by reducing the recirculation and thereby also the loss caused thereby, more power will be available to launch the vehicle.
By reducing the EGR more power is available, wherein the vehicle might be able to launch in a higher gear. The benefits of a higher gear compensates for the reduction of the EGR, such that the exhaust gas regulations still are fulfilled. Further, the reduction of the EGR is performed during such a short period, that the effects thereof in the sense of emissions is negligible, especially since the use of a higher launching gear can compensate for the increase in emissions, such that the emissions from the whole launching procedure is reduced.
In another advantageous embodiment of the invention, the method further comprises a step of reducing the EGR during the whole launch of the vehicle. The launch of the vehicle is defined as the time interval from the starting of the engagement of the starting clutch up to the first gear change after initiated launch. By reducing the EGR more power is available, wherein the vehicle might be able to launch in a higher gear. The benefits of a higher gear compensates for the reduction of the EGR, such that an exhaust gas regulations still is fulfilled. And the reduction of the EGR is performed during such a short period, that the effects thereof in the sense of emissions is negligible.
The method further comprises a step of evaluating the launch of the vehicle, wherein the launch of the vehicle is evaluated in respect of how the expected speed, acceleration, clutch engagement, and gear changes corresponds to the actual launching procedure. After every launch of the vehicle, the lapse of the launch is evaluated and compared to the expected lapse of the launch, wherein any deviations from the expected lapse of the launch are used to optimise the next launch of the vehicle.
In an advantageous variant of the inventive method, the method further comprises a first and a second emergency launch measure, wherein a first emergency measure is an increase of a torque limit of the engine set by a smoke limiter. The smoke limiter is set to minimize the smoke out of the exhaust pipes of the vehicle. By increasing this torque limit during the launch or parts of the launch, more power is available from the engine of the vehicle, wherein a launch of the vehicle is made possible. After the launching procedure, the torque limit set by the smoke limiter is adjusted to its normal value.
A second emergency measure is to increase a torque limit of the engine set by an axle protection limit. The torque limit is set to not overload the axle of the vehicle. The axle of the vehicle is dimensioned for a certain load and lifetime, wherein a safety margin thereby is included. This torque limit is however set with a margin, such that a higher load can be applied to the axle without any harm made. However, this can only be done a limited number of times and during a limited time period.
The method steps of increasing the torque limit of the engine set by the axle protection limit and/or the smoke limiter is an emergency measure, which is to use if the vehicle is not able to start at the lowest gear. Such an emergency might for example occur if the vehicle is heavily loaded and has to be started in an uphill slope.
In order to protect the axle of the vehicle, the method can further comprise the step of counting the number of times the torque limit of the axle is increased and thereafter exceeded during the launching procedure. Wherein the method step of increasing the torque limit of the axle is permanently eliminated from the method when said torque limit is increased and exceeded a predefined number of times. By introducing this counter and a maximum number of times the torque limit of the axle is allowed to be temporarily increased and exceeded, a long life time of the axle can still be assured and the safety of the vehicle is maintained.